Hello Emmanuel,
First, note that Springer will publish the ARM, not the AARM. And yes, you will be able to order a copy directly from Springer. Ada-Europe members will also be able to join a group order that we’re organizing (see for example my recent tweet with a picture of the info page and QR code on display at the Ada-Europe booth in Lisbon to indicate interest).
Ada-Europe did not distribute RMs in Springer LNCS format at its conferences, though has organized bulk orders for previous editions. That’s probably what you remember about the 2005 RM.
Finally, unfortunately there will not be an Ada 2022 Rationale (though there’s indeed a less ambitious “Ada 2022 Overview” document by Jeff Cousins). FYI, I included the following sentence in Ada-Europe’s report to ISO WG9 for the meeting yesterday: “In continuation of its established practice, Ada-Europe undertook to support the production of this new dedicated LNCS issue [of the Ada RM]. The production of an accompanying Rationale has been scrapped instead owing to the lack of material and energy.”
Hope this answers your questions,
Dirk